This invention relates to an engine protection device of the type which is adapted cut off fuel supply to the engine in the event that oil pressure falls below a predetermined value or other parameters of the engine indicating malfunction.
Generally a valve of the aforementioned type is installed into the fuel pipe on the pressure side of the fuel transfer pump between the fuel filters and an injector pump. Typically these valves have three chambers. A high pressure fuel chamber (first chamber), an air chamber (second chamber) that is vented by a breather hole to atmosphere, and an oil chamber (third chamber.) A Spring loaded piston moves within these chambers under the influence of engine oil pressure. Each chamber is separated from the others by seals fitted to the piston or in the body of the valve. Each time the engine starts or stops the piston in the valve moves relative to a valve seat in the chamber to either close off fuel flow through the valve or allow fuel flow to take place. This movement of the piston causes air to be expelled or drawn into the second chamber via the breather hole. This system has a number of disadvantages. Firstly, air which is drawn into the valve, via the breather hole, carries dust and like impurities which settle on seals causing wear. Generally a small filter will be fitted to the breather hole. The filter needs to be replaced regularly but, hi practice, it is found that this is not done and the breather hole becomes clogged which can hamper operation of the valve.
A second problem is that the seals on the piston are unlubricated resulting in high wear and short life. Should one or more of these seals fail, oil and/or fuel is then able to pass into the air chamber from where it exits via the breather hole onto the engine. This can be dangerous and tends to mess the engine.